The shielding effect of heterosubstituents in 13C nuclear magnetic resonance

1976 ◽  
Vol 54 (4) ◽  
pp. 632-641 ◽  
Author(s):  
H. Beierbeck ◽  
J. K. Saunders
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Shifts ◽  
Shielding Effect ◽  
Dihedral Angles ◽  
13C Nuclear Magnetic Resonance ◽  
Shielding Effects ◽  
Nuclear Magnetic

The effect of a heterosubstituent X on 13C chemical shifts, in conformations characterized by dihedral angles of 60°, is analyzed in terms of α-shifts, heteroatom–carbon (XC), hydrogen–heteroatom (HX) and carbon–heteroatom (CX) gauche interactions, and nonbonded γ(X) and δ(X) interactions. The more general parameters [Formula: see text] describe the β-heteroatom shifts in conformations in which the dihedral angles [Formula: see text] differ from 60°. The shielding effects of chlorine, exocyclic oxygen, and endocyclic nitrogen are analyzed.

The stereochemical dependence of 13C nuclear magnetic resonance chemical shifts and 13C–31P couplings in some dialkylphosphonocyclohexanes

1977 ◽  
Vol 55 (4) ◽  
pp. 604-611 ◽  
Author(s):  
Gerald W. Buchanan ◽  
John H. Bowen
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Dihedral Angle ◽  
Chemical Shifts ◽  
Pentavalent Phosphorus ◽  
Angle Dependence ◽  
13C Nuclear Magnetic Resonance ◽  
Shielding Effects ◽  
Nuclear Magnetic

13C chemical shifts and 13C–31P couplings are reported for 15 dialkylphosphonocyclohexanes. Data are compared to those for three related hydroxyphosphonates. Both direct and vicinal 13C–31P couplings are useful stereochemical probes. Materials with equatorial phosphorus exhibit one bond couplings larger by ca. 5 Hz than their axial counterparts. Vicinal couplings follow an approximate dihedral angle dependence but are attenuated by OH substitution. In addition to the expected gauche-γ shielding effects, pentavalent phosphorus substituents induce minor (ca. 1 ppm) upfield shifts at carbons to which they bear an anti-periplanar relation.

Semiempirical calculation of 13C nuclear magnetic resonance chemical shifts of acyclic hydrocarbons. Application to the stereochemical analysis of steroidal side chains

1988 ◽  
Vol 66 (1) ◽  
pp. 71-75 ◽  
Author(s):  
Manuel Gonzalez-Sierra ◽  
Daniel A. Bustos ◽  
Edmundo A. Ruveda ◽  
Alejandro C. Olivieri ◽  
Mariano Grasselli
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Shifts ◽  
Side Chains ◽  
Stereochemical Analysis ◽  
Microcomputer Program ◽  
Semiempirical Approach ◽  
13C Nuclear Magnetic Resonance ◽  
Acyclic Hydrocarbons ◽  
Nuclear Magnetic

A semiempirical approach for predicting 13C nuclear magnetic resonance chemical shifts of acyclic hydrocarbons has been adapted to a microcomputer program. A series of methyl and dimethyl substituted cholesterols has been studied using this program, and the predicted shifts are in agreement with literature reports. Preferred conformations of the steroidal side chains have been also predicted and agree with previous studies. A simple rule for analyzing the trends in the chemical shift of the carbon C-20, which is sensitive to changes in the configuration at C-22, is also given, not only for hydrocarbon side chains but also for hydroxy substituted compounds.

Configurationally dependent hydroxyl group effects on 13C nuclear magnetic resonance chemical shifts of olefinic carbons in cyclic six-membered allylic alcohols

1988 ◽  
Vol 66 (12) ◽  
pp. 3128-3131 ◽  
Author(s):  
Teodoro S. Kaufman
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Hydroxyl Group ◽  
Allylic Alcohols ◽  
Stereochemical Assignment ◽  
13C Nuclear Magnetic Resonance ◽  
Group Effects ◽  
Nuclear Magnetic

The differences in chemical shifts of olefinic carbons, Δδ(sp2), of pseudoequatorial and pseudoaxial six-membered allylic alcohols were correlated with the Δδ(sp2) values of their parent olefins. The results obtained reflect configurationally dependent substituent effects, the magnitude of which could be used for the stereochemical assignment of the hydroxyl group in these compounds.

13C nuclear magnetic resonance and reactivity of 4H-3,1-benzoxazin-4-ones

1988 ◽  
Vol 66 (3) ◽  
pp. 416-419 ◽  
Author(s):  
Valerie J. Robinson ◽  
Robin W. Spencer
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Shifts ◽  
Resonance Assignments ◽  
Human Leukocyte ◽  
Leukocyte Elastase ◽  
13C Nuclear Magnetic Resonance ◽  
Tissue Degradation ◽  
Alternate Substrate ◽  
Nuclear Magnetic

Complete carbon-13 nuclear magnetic resonance assignments have been made for 22 4H-3,1-benzoxazin-4-ones. These compounds are alternate substrate inhibitors of human leukocyte elastase, a serine protease involved in tissue degradation. Correlations between the carbon chemical shifts and rates of alkaline hydrolysis are consistent with hydrolysis via attack at C4, and are also useful in the selection of parameters for structure–activity analysis.

15N and 13C nuclear magnetic resonance of deoxydinucleotide monophosphates. I. Protonation of deoxycytidylyl-(3′,5′)-guanosine in dimethylsulfoxide

1988 ◽  
Vol 66 (10) ◽  
pp. 2492-2497 ◽  
Author(s):  
Giovanna Barbarella ◽  
Massimo Luigi Capobianco ◽  
Antonio Carcuro ◽  
Francesco Paolo Colonna ◽  
Anna Garbesi ◽  
...  
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Sodium Salt ◽  
Chemical Shifts ◽  
Phosphate Anion ◽  
13C Nuclear Magnetic Resonance ◽  
Nuclear Magnetic

The 15N and 13C chemical shifts of the sodium salt of deoxycytidylyl-(3′,5′)-guanosine have been measured in dimethylsulfoxide in the presence of variable amounts of CF3COOH. N3(cyt) is protonated first, followed by N7(gua) and the phosphate anion. These results vary from those reported for the binding of the methylmercuric cation to d(CpG).

13C Nuclear Magnetic Resonance of Oximes. I. Solvent and Isotope Effects on the 13C Chemical Shifts of Acetoxime

1972 ◽  
Vol 50 (12) ◽  
pp. 1956-1958 ◽  
Author(s):  
N. Gurudata
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Shift ◽  
Solvent Effects ◽  
Chemical Shifts ◽  
Isotope Effects ◽  
Solvent Interactions ◽  
13C Chemical Shifts ◽  
13C Nuclear Magnetic Resonance ◽  
Nuclear Magnetic

The 13C n.m.r. spectrum of acetoxime has been obtained in five representative solvents and the chemical shifts of the three carbon atoms measured. The solvent effects on the chemical shifts are found to reflect specific solute–solvent interactions. The effect of deuteration of the α-protons on the chemical shift of the oximino carbon is also discussed.

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